Hey,
Welcome to Apple Support Communities.
From what I gather, there’s an iCloud Backup alert on your iPad mini that won’t go away when you tap OK. If you haven’t already, take a look at the article linked below and try the touchscreen troubleshooting suggestions that it provides.
If the screen on your iPhone, iPad, or iPod touch doesn't respond to touch - Apple Support
Also, you can find more information about the iCloud Backup alert here:
iCloud Backup alert messages - Apple Support
Ciao,
-Jason